Offset calibration system and method of automatic power control loop

ABSTRACT

An offset calibration system of a control loop at least comprises a pre-amplifier circuit and a post-amplifier circuit. The pre-amplifier circuit generates a pre-output signal and then transmits the pre-output signal to the post-amplifier circuit to amplify. The offset calibration system comprises a comparator, an offset calibration module, and a determination circuit. The comparator compares the pre-output signal with a predetermined pre-reference signal to generate a pre-compared signal. The offset calibration module stores a predetermined and adjustable offset calibration value for adding to the pre-output signal. The determination circuit adjusts the offset calibration value based on the pre-compared signal, so the offset calibration value can be added to the pre-output signal dynamically to compensate and calibrate the offset of the pre-output signal caused by the pre-amplifier circuit to avoid the post-amplifier circuit amplifying the offset of the pre-output signal again.

FIELD OF THE INVENTION

[0001] The present invention relates to an offset calibration system andmethod of an automatic power control loop for calibrating the offsetgenerated by the automatic power control loop.

BACKGROUND OF THE INVENTION

[0002] When the pickup head of an optical information recording/readingapparatus writes and reads pits of a compact disk, an automatic powercontrol loop is used to control and adjust the laser power of the laserdiode within the pickup head. A pickup head comprises a laser diode, alaser diode driver and a laser power detector. The laser diode providesa laser source to read or write data on the compact disk. The laserpower detector detects the laser power of the laser beam to output acorresponding laser power detection signal.

[0003] The pickup head uses different laser powers when it is writing orreading. The power in writing is higher than the power in reading. It isimportant to control the power of the laser emitted by the laser diode.The laser diode is driven by the laser diode driver. Hence, controllingthe laser diode driver can further control the laser power.

[0004] The automatic power control loop controls the laser diode driverto output an electric current to drive the laser diode for emitting alaser bean with an adequate laser power. The laser power detectionsignal outputted by the laser power detector and the laser power of thedetected laser beam are in inverse proportion. The laser power detectionsignal will be sampled and held by a sample/hold circuit of theautomatic power control loop, and then transmitted to a pre-amplifierfor amplifying and generating a pre-output signal. The pre-output signalis subtracted by a predetermined reference signal in an adder. If theresult value does not equal to zero, the laser power of the laser beamstill needs to be adjusted. A post-amplifier can adjust the pre-outputsignal and generate a power control signal. The post-amplifier transmitsthe power control signal to the laser diode driver for emitting anadequate laser power. In an ideal condition, when the laser diodedoesn't emit the laser beam, the pre-output signal is the predeterminedreference signal.

[0005] In general, the prior art control and calibration method for thelaser power emitted by the laser diode can adjust the laser power verywell. However, in the prior art, when the laser power detector generatesthe laser power detection signal with an offset, the automatic powercontrol loop can't calibrate immediately. Through the amplifier, theoffset is amplified and may be beyond the range that the adder canadjust. Therefore, a wrong power control signal is produced resulting ina wrong laser power. Consequently, mistakes occur in writing/readingdata of the compact.

SUMMARY OF THE INVENTION

[0006] It is therefore a primary objective of the present invention toprovide an offset calibration system and method of an automatic powercontrol loop for calibrating a laser power emitted from a laser diode sothat the laser diode can emit accurate laser power.

[0007] The automatic power control loop of the present inventioncomprises a preamplifier circuit and a post-amplifier circuit. Thepre-amplifier circuit generates a pre-output signal and then transmitsthe pre-output signal to the post-amplifier circuit for amplifying. Theoffset calibration system comprises a comparator, an offset calibrationmodule and a determination circuit. The comparator compares thepre-output signal with a predetermined pre-reference signal to generatea pre-compared signal. The offset calibration module stores apredetermined and adjustable offset calibration value for adding to thepre-output signal. The determination circuit electrically connects tothe comparator and the offset calibration module to adjust the offsetcalibration value stored in the offset calibration module based on thepre-compared signal generated by the comparator.

[0008] The determination circuit adjusts the offset calibration valuedynamically based on the pre-compared signal, so the offset calibrationvalue can be added to the pre-output signal dynamically to compensateand calibrate the offset of the pre-output signal caused by thepre-amplifier circuit. That will avoid the post-amplifier circuitamplifies the offset of the pre-output signal again.

[0009] The present invention calibrates the offset of an automatic powercontrol loop by the offset calibration system. The offset of thepre-output signal can be compensated and calibrated immediately by theoffset calibration system of the present invention to avoid that thepost-amplifier circuit amplifies the offset of the pre-output signalagain.

[0010] These and other objectives of the present invention will no doubtbecome obvious to those of ordinary skill in the art after the followingdetailed description of the preferred embodiment, which is illustratedin the various figures and drawings.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

[0011]FIG. 1 is the block diagram according to the offset calibrationsystem of the automatic power control system in the present invention.

[0012]FIG. 2 is the block diagram of the pre-amplifier circuit and thepost-amplifier circuit according to FIG. 1.

[0013]FIG. 3 is the flow chart of the automatic power control loop andthe offset calibration system of the present invention according to FIG.1 and FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Please refer to FIG. 1. FIG. 1 is a block diagram of an offsetcalibration system 20 of an automatic power control system 1 accordingto the present invention. The present invention is an offset calibrationsystem 20 of a control loop 1. The control loop 1 comprises apre-amplifier circuit 10 and a post-amplifier circuit 11. Thepreamplifier circuit 10 generates a pre-output signal S1 and thentransmits the pre-output signal S1 to the post-amplifier circuit 11 toamplify. The control loop 1 is an automatic power control loop tocontrol a laser source device 30.

[0015] The laser source device 30 comprises a laser diode 32 and a laserdiode driver 31. The automatic power control loop 1 controls the laserdiode driver 31 to output a driving electric current to drive a compactdisk system (not show in FIG. 1) with the laser beam when the compactdisk system reads or writes a compact disk. The compact disk systemcomprises a pickup head which comprises a laser power detector to detecta laser power of the laser beam, and to ouput a corresponding laserpower detection signal. The laser power detection signal and thedetected laser power of the laser beam are in inverse proportion.

[0016] The offset calibration system 20 of the present inventioncomprises a comparator 22, an offset calibration module 24, adetermination circuit 26, and a pre-adder 28. A comparator 22 comparesthe pre-output signal S1 with a predetermined pre-reference signal Srefto generate a pre-compared signal S2. The offset calibration module 24stores a predetermined and adjustable analog offset calibration valueAOC for adding to the pre-output signal S1. The determination circuit 26electrically connects to the comparator 22 and the offset calibrationmodule 24 to adjust the analog offset calibration value AOC stored inthe offset calibration module 24 based on the pre-compared signal S2generated by the comparator 22. The pre-adder 28 makes the analog offsetcalibration value AOC add to the pre-output signal S1 to become acalibrated pre-output signal SC, and then transmits the calibratedpre-output signal SC to the post-amplifier circuit 11.

[0017] The determination circuit 26 adjusts the analog offsetcalibration value AOC dynamically based on the pre-compared signal S2,so the analog offset calibration value AOC can be added to thepre-output signal S1 dynamically to compensate and calibrate the offsetof the pre-output signal S1 caused by the pre-amplifier circuit 10 toavoid that the post-amplifier circuit 11 amplifies the offset of thepre-output signal S1 again.

[0018] The offset calibration module 24 comprises a pre-register 241 anda pre-D/A converter 242. The pre-register 241 stores a digital offsetcalibration value DOC. The pre-D/A converter 242 converts the digitaloffset calibration value DOC to a corresponding analog offsetcalibration value AOC. The analog offset calibration value AOC will besent to the pre-adder 28, and then added to the pre-output signal S1.

[0019] In an ideal situation, when the laser diode 32 doesn't emit thelaser beam, the pre-output signal S1 generated by the pre-amplifiercircuit 10 is the predetermined pre-reference signal Sref. Only when thelaser diode 32 doesn't emit the laser beam, the determination circuit 26will adjust the offset calibration value based on the pre-comparedsignal S2 to make the pre-adder 28 add the analog offset calibrationvalue AOC to the pre-output signal S1 for compensating and calibrating.

[0020] Please refer to FIG. 2. FIG. 2 is a block diagram of thepre-amplifier circuit 10 and the post-amplifier circuit 11 shown inFIG. 1. The pre-amplifier 10 comprises a sample/hold circuit 12 and apre-amplifier 14. The sample/hold circuit 12 samples and holds the laserpower detection signal according to a control signal, and outputs asample/hold signal S/h. The pre-amplifier 14 receives and amplifies thesample/hold signal S/h outputted from the sample/hold circuit 12 togenerate the pre-output signal S1. The pre-output signal S1 then isinputted to the offset calibration system 20 of the present inventionfor calibrating the offset.

[0021] As shown in FIG. 2, the calibrated pre-output signal SC isinputted to the post-amplifier circuit 11. The post-amplifier circuit 11provides a power control signal SP to control a laser diode driver 31 ofthe laser source device 30. The post-amplifier circuit 11 comprises apost-register 13, a post-D/A converter 15, a post-subtractor 17, and apost-amplifier 19. The post-register 13 stores a digital poweradjustment value. The post-register 13 comprises a plurality of storageunits to store the digital power adjustment value, and the number ofstorage units in the post-register 13 determines the range of thedigital power adjustment value. The determination circuit 26 in FIG. 1adjusts the offset calibration value according to the pre-comparedsignal S2 to make the analog offset calibration value AOC added to thepre-output signal S1 to avoid the pre-output signal S1 being beyond therange of the power adjustment value in the post-register 13.

[0022] The post-D/A converter 15 converts the digital power adjustmentvalue to a corresponding analog power adjustment value. Thepost-subtractor 17 adds the analog power adjustment value to thecalibrated pre-output signal SC to become a post-output signal S3. Thepost-amplifier 19 receives and amplifies the signal from thepost-subtractor 17 to generate the power control signal SP. The powercontrol signal SP can control the laser diode driver 31, and furthercontrol the laser power of the laser beam emitted from the laser diode32.

[0023] Please refer to FIG. 3. FIG. 3 is a flow chart of the automaticpower control loop 1 and the offset calibration system 20 of the presentinvention according to FIG. 1 and FIG. 2. The method comprises thefollowing steps:

[0024] Step S31: sampling and holding a laser power detection signalaccording to a control signal, and outputting a sample/hold signal S/h;

[0025] Step S32: amplifying the sample/hold signal S/h to generate apre-output signal S1;

[0026] Step S33: storing a digital offset calibration value DOC;

[0027] Step S34: comparing the pre-output signal S1 with a predeterminedreference signal Sref to generate a pre-compared signal S2;

[0028] Step S35: dynamically adjusting the digital offset calibrationvalue DOC according to the pre-compared signal S2;

[0029] Step S36: converting the digital offset calibration value DOC toa corresponding analog offset calibration value AOC;

[0030] Step S37: dynamically adding the analog offset calibration valueAOC to the pre-output signal S1 to become the calibrated pre-outputsignal SC to compensate and calibrate the offset of the pre-outputsignal caused by the pre-amplifier circuit to avoid the post-amplifiercircuit amplifying the offset of the pre-output signal again;

[0031] Step S38: storing a power adjustment value in a digital way;

[0032] Step S39: converting the digital power adjustment value to acorresponding analog power adjustment value;

[0033] Step S40: adding the analog power adjustment value to thecalibrated pre-output signal SC to become a post-output signal S3;

[0034] Step S41: receiving and amplifying the post-output signal S3 togenerate a power control signal SP.

[0035] The present invention utilizes an offset calibration system tocompare and calibrate the pre-output signal generated by thepre-amplifier circuit. The invention makes the offset of the pre-outputsignal calibrated by the offset calibration system before outputted intothe post-amplifier circuit to avoid the pre-output signal with offset tobe transmitted to the post-amplifier circuit, so to avoid the offsetbeing beyond the range of the power adjustment value. After amplifying,the offset will become the larger power control signal. However, theoffset of the pre-output signal has been calibrated by the offsetcalibration system of the present invention, so that mistakes will notoccur when writing/reading data of the compact disk system. This appearsthe advantage and the utility of the offset calibration system in thepresent invention.

[0036] The description of the above-mentioned preferred embodimentsprovides a better understanding on the strengths and spirits of thispresent invention, not to limit the domain of the invention. Moreover,it aims to include various modification and arrangement parallel in forminto the domain of the patent applied by this present invention. Due tothe above mention, the domain of the patent applied by the inventionshould be explained in a macro view to cover all kinds of possiblemodification and arrangement of equal form.

What is claimed is:
 1. An offset calibration system of an automaticpower control loop which at least comprises a pre-amplifier circuit anda post-amplifier circuit, said pre-amplifier circuit generating apre-output signal and then transmitting said pre-output signal to thepost-amplifier circuit to amplify, said offset calibration systemcomprising: a comparator for comparing said pre-output signal with apredetermined pre-reference signal to generate a pre-compared signal; anoffset calibration module for storing a predetermined and adjustableoffset calibration value; a determination circuit for electricallyconnecting to said comparator and said offset calibration module, andadjusting said offset calibration value stored in said offsetcalibration module based on said pre-compared signal generated by saidcomparator; and a pre-adder for making said offset calibration valueadded to said pre-output signal; wherein said determination circuitadjusts said offset calibration value dynamically based on saidpre-compared signal, so said offset calibration value can be added tothe pre-output signal dynamically to compensate and calibrate the offsetof said pre-output signal caused by said preamplifier circuit to avoidsaid post-amplifier circuit amplifying the offset of said pre-outputsignal again.
 2. The offset calibration system according to claim 1,wherein said automatic power control loop is used for controlling alaser source device which comprises a laser diode and a laser diodedriver, and said automatic power control loop controls said laser diodedriver to output a driving electric current to drive said laser diodewhich emits a corresponding laser beam.
 3. The offset calibration systemaccording to claim 2, wherein said laser diode provides a compact disksystem with said laser beam when said compact disk system reads orwrites a compact disk, said compact disk system comprising a pickup headwhich comprises a laser power detector to detect a laser power of saidlaser beam reflecting from said compact disk, and output a correspondinglaser power detection signal.
 4. The offset calibration system accordingto claim 3, wherein said pre-amplifier circuit comprises: a sample/holdcircuit for sampling and holding said laser power detection signalaccording to a control signal; and a pre-amplifier for receiving andamplifying the signal outputted from said sample/hold circuit togenerate said pre-output signal.
 5. The offset calibration systemaccording to claim 3, wherein said laser power detection signaloutputted from said laser power detector and said detected laser powerof said laser beam are in inverse proportion.
 6. The offset calibrationsystem according to claim 2, wherein in an ideal condition, when saidlaser diode doesn't emit said laser beam, said pre-output signalgenerated by said pre-amplifier circuit is said predeterminedpre-reference signal.
 7. The offset calibration system according toclaim 6, wherein when said laser diode doesn't emit said laser beam,said determination circuit will adjust said offset calibration valuebased on said pre-compared signal to make said offset calibration valueadded to said pre-output signal for compensating and calibrating.
 8. Theoffset calibration system according to claim 1, wherein said offsetcalibration module comprises: a pre-register for storing said offsetcalibration value digitally; and a pre-D/A converter for converting saiddigital offset calibration value to a corresponding analog offsetcalibration value to be sent to said pre-adder.
 9. The offsetcalibration system according to claim 1, wherein said post-amplifiercircuit, which provides a power control signal to control said laserdiode driver, comprises: a post-register for storing a digital poweradjustment value; a post-D/A converter for converting said digital poweradjustment value to a corresponding analog power adjustment value; apost-subtractor for adding said analog power adjustment value to saidpre-output signal; and a post-amplifier for receiving and amplifying thesignal from said post-subtractor to generate said power control signal.10. The offset calibration system according to claim 9, wherein saidpost-register comprises a plurality of storage units to store saiddigital power adjustment value, and the number of storage units in saidpost-register determines the range of said digital power adjustmentvalue.
 11. An offset calibration method of an automatic power controlloop which at least comprises a pre-amplifier circuit and apost-amplifier circuit, said pre-amplifier circuit generating apre-output signal and then transmitting said pre-output signal to thepost-amplifier circuit to amplify, said offset calibration methodcomprising: Comparing said pre-output signal with a predeterminedpre-reference signal to generate a pre-compared signal; Dynamicallyadjusting a pre-stored offset calibration value according to saidpre-compared signal; and Dynamically adding said offset calibrationvalue to said pre-output signal to compensate and calibrate the offsetof said pre-output signal caused by said pre-amplifier circuit to avoidsaid post-amplifier circuit amplifying the offset of said pre-outputsignal again.
 12. The offset calibration method according to claim 11,wherein said automatic power control loop is used for controlling alaser source device which comprises a laser diode and a laser diodedriver, and said automatic power control loop controls said laser diodedriver to output a driving electric current to drive said laser diodewhich emits a corresponding laser beam.
 13. The offset calibrationmethod according to claim 12, wherein said laser diode provides acompact disk system with said laser beam when said compact disk systemreads and writes a compact disk, said compact disk system comprising apickup head which comprises a laser power detector to detect a laserpower of said laser beam reflecting from said compact disk, and ouput acorresponding laser power detection signal.
 14. The offset calibrationmethod according to claim 13, wherein said method further comprises:sampling and holding said laser power detection signal according to acontrol signal; and amplifying said laser power detection signaloutputted from said sample/hold circuit to generate said pre-outputsignal.
 15. The offset calibration method according to claim 13, whereinsaid laser power detection signal outputted from said laser powerdetector and said detected laser power of said laser beam are in inverseproportion.
 16. The offset calibration method according to claim 12,wherein in an ideal condition, when said laser diode doesn't emit saidlaser beam, said pre-output signal generated by said pre-amplifiercircuit is said predetermined pre-reference signal.
 17. The offsetcalibration method according to claim 16, wherein when said laser diodedoesn't emit said laser beam, said offset calibration value is adjustedbased on said pre-compared signal to make said offset calibration valueadded to said pre-output signal for compensating and calibrating. 18.The offset calibration method according to claim 11, wherein the offsetcalibration method further comprises: storing said offset calibrationvalue digitally; and converting said digital offset calibration value toa corresponding analog offset calibration value to be added to saidpre-output signal.
 19. The offset calibration method according to claim11, wherein said post-amplifier circuit provides a power control signalto control said laser diode driver by the following steps: storing adigital power adjustment value; converting said digital power adjustmentvalue to a corresponding analog power adjustment value; adding saidanalog power adjustment value to said pre-output signal; and receivingand amplifying said pre-output signal added to said analog poweradjustment value to generate said power control signal.
 20. The offsetcalibration method according to claim 19, wherein said post-amplifiercircuit comprises a post-register which has a plurality of storage unitsto store said digital power adjustment value, and the number of saidstorage units in said post-register determines the range of said digitalpower adjustment value.